Multistage fan



March 8; 1938.

A. E. SEELIG MULTISTAGE FAN 2 sheets-sheet 1 v @alffd Original FiledApril 26, 1935 /NL HvTo/e i? A TiOR/VEY March 8, 1938.

' MAX. DESIRED HP A. E. SEELK;

MULTISTAGE FAN original Filed Apil 2e, 1935' 2 sheets-sheet f2 I C n s*QQ XC Hamed asuoH o Cubic Feel' u: Minu'z 5g/mdf.

El ATTORNEY Reissued Mar. 8., 1938 JNITED ISTATES` Rr.Y 26,668

PATENT oil-FICE No. 18,326, April 26, 1935.

Application fork reissue April zo, 1931, serial No. 138,521

' 2z claims. l(orazio-114) This invention relates to propeller fans andparticularly to a load linliting air delivery pressure volume regulatingmeans and combined following stage air guide vanelto effectivelymultistage propeller fans.

Propeller fans are used in the art for varied purposes, as for exampleto supply air for fuel combustion in furnaces, for drying, for airconditioning and for ventilation or for other uses where high volumes ofair at relatively low static pressures are desired.- v l 'I'he volume ofair and the pressure at which it is delivered are proportional, among;other things, to the diameter of the fan -and the rate l5 at which itrevolves. It Will be apparent that for increased air deliveryvolumes andincreased air delivery pressures, it is necessary to increase either thespeed of rotation of the fan orI its diameter, or both.

standpoint of mechanical design and the reduction of attendant noise ofoperation, it is not desirable to increase the diameter of the fan andits`rotational speed beyond certain limits.

In order, therefore, to increase the delivery volume and pressures dfsuch fans while at the same time limiting the speed and diameterthereof, I arrange a plurality of fans on a common drive shaft in seriesin a common conduit to thereby provide a multi-stage fan, having two ormore stage fans, each succeeding fan to act as a booster for thepreceding fan.

In a propeller fan, the blades of which are of helicoidal design, theresultant motion imparted to each particle of air while generallyforward is also rotational andis in the nature of a forward movingspiral.

It will be apparent, therefore, that in multistage fans, since eachsubsequent or following stage fan operates at the same speed and in thesame rotative direction as the preceding stage fan, the column of airleaving the preceding stage fan will have imparted to it a rotary motionhaving substantially the same rotary speed and rotary direction as thatof the following stage fan.

It will, at once, be seen that the following stage fan can react onlyslightly or perform very little work on the air delivered to it, and towhip or push it forward, since both the fan and air are rotating in asimilar rotative direction at substantially the same speed. It isreadily apparent, therefore, that multi-staging the fans will not, ofitself, result in the delivery of increased air volumes and pressures,since it becomes necessary to so present the air delivered by thepreceding It is apparent that, from la.v

fank to the following stage fan. that the following stage will therebyreact and perform work on the air and to thereby increase its forwardvelocity and thereby the volume and pressure at which it is finallydelivered from the multi-stage 5 fan.

The present invention, therefore, contemplates the provision of meanswhereby propeller fans may be effectively multi-staged. f

I have found that by changing the motion of 10 the air as it isdelivered by the preceding fan from a forward rotational direction toakforward direction parallel to the axis .of the leading fan, withoutsubstantially reducing the speed of air flow, the leading fan may theneffectively react'l and perform work on the air so delivered to it,whereby the air volume .and pressures delivered by such a multi-stagefan are substantially increased by each additional stage which isprovided. y 2o It will readily b e understood that the magnitude of suchforward rotational motion of the air delivered from a preceding fan maybe varied, thereby varying the eil'ectiveness of the following fan uponthe air delivered toit and conse- 25 quently varying th'e air volumeland pressure delivered by the multi-stage ian as a unit.

A novel and simple pressure volume regulator for multi-stage fans may-accordingly be arranged by providing means for varying the mag- 30nitude of the rotational motion of the air directed to the followingstage fan,'the provision of which the present invention furthercontemplates.

The volume of air and the pressure delivered by propeller type fans maybe varied by either 35 changing the speed of rotation of the fan, by theuse of a variable speed motor, or by maintaining a constant speed ofrotation of the fan and restricting the air flow from the farl by meansof a damper. 40

Constant speed motors are'simpler in construetion, more dependable inoperation and less cost-1 ly than variable speed motors, operating athigh speeds, especially for use with alternating current, and thepresent invention is particularly di- 45 rected to the regulation ofmulti-stage propeller fans driven by constant speed electric motors.

Since constant speed motors are. mechanically more desirable to drivepropeller fans, and therefore most frequently used in the art,regulation 50 of the air volume and pressure by means of dampersinserted in the air conduits, which increase the resistance to the airflow on the fan delivery side to thereby decrease the air volumedelivered, are most usually encountered in practice.A 55

Such damper vcontrolled constant speed propeller fans generallyheretofore found in the art,

place an increased horsepower load on the driving motor as the deliveryvolume is decreased,

in the art, requires comparatively large capacity motors due to the factthat closingof the damper would overload the motor capacity selected tomeet the requirement of maximum air delivery with wide open damper.

'I'he present invention, therefore, further contemplates the provisionof air volume regulating means for combination with constant speed motor-driven multi-stage propeller fans, which, within the predetermined airvolume operating limits of the fans, provides a decreasing1 horsepowercharacteristic with decreasing volumes of air ow delivered and whichregulating means are arranged to limit the minimum air volume deliveredand therefore the maximum horsepower load which can be placed on thedriving motor.

The various objects of my invention will be clear from the descriptionwhich follows and from the drawings in which Fig. 1 is a side elevationand partial section of my new multi-stage fan, showing the combinedguide and pressure volume regulating vanes.

Fig. 2 is a sectional view of the same taken on the line 2 2 of Fig. 1.

Fig. 3 is front sectional elevation, showing the guide vanes in fullyclosed position.

Fig. 4 is a partial side elevation of my new multi-stage fan, and guidevane regulating means.

Fig. 5 is a partial sideb elevation of a modification of my invention.

Fig. 6 is a section taken on the line 8 6 of Fig. 5.

Fig. 7 is a partial plan view of'a further modiiication of invention.

Fig. 8 is a section' on the line 8 8 of Fig. '7.'

Fig. 9 is a fro'nt elevation of a modification of. my novel guide vanes.

Fig. 10 is a graph of the pressure, volume and horsepowercharacteristics of a multi-stage fan Vconstructed in accordance with myinvention.

In that practical embodiment of my invention which I have illustrated byway of example in Figs. 1 to 4 inclusive, a constant speed electricmotor l0, for driving the propeller fans i2 and I4, is supported in thefan casing I 6 on the motor cradle I 8, which is secured to the casingin any suitable manner, a's for vexample by means of bolts 20. y

'Ihe motor shaft 22 extends from both sides of the motor body to receivethe propeller fans,y

as by a key and key way, well knownin the art and which therefore neednot be described in detail. l

It will be understood thatlthe motor need not be positioned intermediatethe fans, but may be positioned -in any convenient place to drive thev,fantis"as for example,"o\tside the casing and opeii'atlvely 'connectedto the fans, either directly or indirectly, as by means of suitablegears or belts and pulleys.

As the motor drives the fans, air is drawn into the casing by the motionof the rst fan I2, which whips and pushes the air before it impartingthereto a generally forward spiral motion, having substantially the samerotary direction as the tan Il. Since the following stage fan I4 issimilar to the first stage fan I 2 and operates at the same speed, itwill be apparent that the followingstage fan does not effectively reactor perform work on the air delivered to it and does not substantiallyimpart any further motion thereto, since both the following fan and theair delivered to it rotate substantially in the same direction and atthe same speed.

In order thereforei,t o change the motion of the air, as it flowsfromthe first stage fan from generally forward spiral direction and toaxially direct it toward the following stage fan, I arrange guide orredirectional vanes 24, radially in the casing, adjacent to and on thedischarge or delivery side of the first stage fan. l'I'he air, as it isdelivered by the first stage fan, has imparted to it a substantiallyforward rotary motion with which it strikes the guide vanes, and flowstherealong and is directed thereby axially toward the s following stagefan, which can then more effectively react and perform work on the airstream directed to it.

Such guide or redirectional vanes may be constructed from sheet metal inthe form of flat plates as shown in Fig. 1. A In order to preventaireddy currents, which may be produced by the ow of air against a iiatplate, or any possible resulting friction loss, streamlined guide vanesl25, shown in Fig. '7, provided with proper curvature, whegreby thedirection of the air'owing along the lguide vanes may be graduallychanged without formation of eddy currents or attendant friction lossmay be supplied. l

If desired. such guide vanes may take the form of interlaced at platesor wires 216, asa honeycomb or egg crate, shown in Fig. 9 or variousother shapes. v

'Ihe fans may be arrangedon the motor shaft as close together as thesize of ,their common motor drive will permit, the guide vanes,preferablyl being arranged as nearly adjacent to the first stage fan asis possible.

It will be apparent that the delivery effective- `ness.of the followingfan on the air delivered to tional motion component of the air directedto the said following fan. It will be seen, therefore, ,that the airvolume vand pressure generated by the following stage fan, may be variedby varying the magnitude of the rotational motion of the air, prior toits delivery to the followingfstage fan.

As such rotational air component is increased,`

the effectiveness of the following -fan will decrease and the airdelivery volume and pressure delivered by the multi-stage fan :willtherefore rotational direction as it leaves the first fan.

vIn order, therefore, to provide a means for varying the4 proportion ofthe air delivered to the following fan with a rotary speed componentsubit is dependent on the magnitude of the rotastantially equal to andin a rotary direction sim-I6 ilar to that of the following fan andthereby decreasing the air delivery of my multi-stage fan as a. unitfrom .the maximum to any desired lower magnitude, I pivotally arrangetheI guide vanes .it ori-the air is less, as the rotary similar to thatof the in the casing so that their position relatively to the followingstage f an may be changed to thereby vary the rotary component of theair directed tc it. v

Inasmuch as the following fan is less effective on the air directed toit and the-work done by air delivery component is increased, it will bereadily seen, that the motor horsepower required to drive the fans willdecrease as the volume is decreased and not increase as heretofore withconstant speed damper controlled fans.

In order to vary the position of the guide vanes and to thereby regulatethe air volume and pressure delivered by the ymulti-stage fan, I secureeach guide vane to a shaft 21 which is pivotally arranged in a socket 2Barranged on the motor body, and thereby adapted to swing or rotate inthe casing in the sockets.

The vane shafts extend through suitable openings 30, arranged in thecasing, and are provided at their upper ends with the horizontal arms32, each having a pin 34 depending therefrom and engaging a slot 36,arranged on a sleeve 40, which is adapted to be rotated on the casingthereabout.

In order to rotatably secure the sleeve on the casing, I -prefer toarrange thereon a plurality of opposed pairs of Z bars 4|, the lowerhorizontal sides 42 of which are secured to the casing in any suitablemanner, such as by rivets 44', and the upper horizontal sides togetherform an annular channel 41 in which the sleeve may be moved on thecasing, the vertical si-des 48, restraining the motion 'of the sleeve torotation about the casing.

A plurality 'of similar slots 36 are circumferentially arranged parallelto Aeach other on the sleeve and divergently disposed to the axisthereof, each slot operatively engaging the pin depending from thehorizontal vane arm and `in which slot the pin may be urged toreciprocate.

As the sleeve is rotated on the casing by the-^ handle bar 5I, extendingupwardly from the sleeve, the pin is urged to move in the slot, causingthe shaft to rotate in the socket, and thereby changing the position ofthe vane relative to the first fan, or any following fan.

The slots are arranged, to` rotate the vanes from a full openpositiontijyvhen the vanes are disposed at right angles tothe first fan,as shown in Fig. 2, in ,which position, air owing from the ilrst fan isdirected by the vanes toward the following fan axially thereof and therotary motion imparted to theair by the first fan, is completelyeliminated and the multi-stage fan delivers its maximum capacity, to thefull closed position when the vanes are disposed parallel to the rstfan, as shown in Fig. 3, in which position the ymulti-stage fan deliversits minimum capacity.

The vanes are preferably arranged to extend completely from the motorbody to. the inner face 53 of the casing, the upper edges 49, of thevanes-being preferably provided with a curvature casing, whereby theupper vane edges will be contiguous to the casing,I when the vanes aredisposed in the full closed position. In Fig. l0, I have shown a graphwhich shows the pressure,V volume and horsepowercharacter- .istics of atwo stage fan constructed in accordance with the present invention.

volume in 46 of the opposed Z bars v `for ventilating purposes,

One series of curves is drawn to show the air cubic feet per minute andthe corresponding pressures delivered by the two stage fan for certainpredetermined guidevane positions, which positions are diagrammaticallyillustrated at the right of the curves.

The pressure volume characteristic curves are k indicated bythe lettersPV, the numeral adjacent the letters signifying the correspondingposition of the guide vanes as illustrated at the right of the curves.

The second series of curves are the horsepower required to deliver thevolume of air at the pressure shown on the rst series of curvescorresponding thereto for the given vane positions. These c'urves areindicated by the letters H13-V, the numeral adjacent the letterssignifying the corresponding position of the guide vanes.

When the guide vanes are turned to the full open, indicate-d as positionl, the pressure volume fan characteristics are shown by the curve, PVIand the corresponding horsepower characteristics by the curve HP-VL Asthe guide vanes are rotated in the casing to assume an arbitraryposition 2, it will be seen that the air straightening action of theguide vanes is reduced and they no not completely eliminate the rotarymotion of the air, thereby makdrawn to show lower pressure volumecharacteristic (PVZ) will ing the'second stage fan less eiective andaf'30 power characteristic (HPVZ) As the guide\vanes are rotated intothe position 3 the magnitude of the rotary component of the air directedto the vfollowing fan is iricreased and the corresponding pressurevolume (PVS) and horsepower (HPV) characteristics are of a still lowermagnitude.

As the guide vanes are still further rotated, toward full closedposition, into arbitrary position 4, the magnitude of the rotary aircomponent is further increased, and in addition the guide vanes nowrestrict the air passage in the manner of a damper, thereby addingresistance to the flow of the air and producing an increasing'resistance to the rotation ofthe fans and a proportional increase in thepower required to drive the fans.

Therefore, a position will be reached, where for a lower pressure volume(PV4) characteristic, the corresponding horsepower characteristic(HP-V4) will be higher and, will rapidly increase, in value and when theguide vanes assume a completely closed position as indicated at 5, thehorsepower (HPVS) will be greater than the maximum desired horsepowercapacity, which would thereby overload the drivingmotor.

Hence, the present invention further contemplates the`provision of meansfor limiting the maximum load which maybe placed von the motor drivingmy multi-stage fan, as the air volume is reduced.

For the purpose of illustration, Iwill further describe my novelmulti-stage fan and volume regulating means as applied to a coal burningboiler for supplying air thereto, though other applications, whereeither forced. or induced draft are desired, as for example fanssupplied will be readily apparent to those skilled in the art. Y

The thicknessof the -fuel bed, for which combustion air is to befurnished by my multi-stage fan, a sudden requirement for quick steamingin the boiler, or other conditions may require the .pressure indicatedat A supply by the fan of the volume of air at the on the curve PVI, wis obtained' with the guide vanes disposed in full open position, thehorsepower requirement for which will be found at A on the curveI-HL-VZ. As the steam inthe boiler is raised to the desired pressure, itwill be apparent that the rate of fuel combustion must be lowered to acombustion rate which will maintain the boiler load, and the steam atthe desired pressure, and therefore a lower air delivery volume isrequired. This may correspond to the pressure volume characteristic B,to obtain which, it is readily seen requires the guide vanes to assumeposition 2 at which position the horsepower required is indicated at B'.By further closing the guide vanes, it is readily seen that a powerpressure and volume C, with a corresponding lower horsepower C' isobtained, until the dampering eect of the guide vanes is encountered,when the horsepower commences to increase, as indicated at D.

It will be readily seen that as the dampering effeet of the guide vanesincreases air volumes and pressures are reached at which the horsepowerincreases until it exceeds the maximum desired horsepower, namely themotor capacity.

It then becomes necessary to limit the reduction in the quantity of airdelivered so that the motor' will notbe overloaded. The presentinvention therefore further contemplates the combination with therotatable guide vanes of means for lim-7 vdelivered by a iting themagnitude delivered and thereby limiting the may be applied to the motordrive.

When the air passage is completely closed by the guide vanes, neitherfan can deliver any airand the horsepower load on the driving motor willbe at a maximum, and it will be .understood that this maximum load maybe avoided by arranging the guide vanes in suchiashion that the entireair passage is never completely closed or restricted. v

I accomplish such load limitation by constructing the guide vanes of asize such that, as the vanes are rotated into the full closed position,shown in Fig. 3, they are appreciably spaced from each other, to providethe air release pas-. sages 58. The proportional total area of these airrelease passages to the total area of the guide vanes may be varied asdesired, but should be arranged to limit the pressure volume deliveredwhen 4the guide vanes are completely closed to the magnitudes set forthat L/on the PV regulation curve, thereby limiting the load on the. motorto the maximum desired horsepower.

The closure of the air passage may likewise be restrictediby providing aStop pin 52 on the inner wall 5I of the casing, therebyf limiting therotation of the guide vanes-and preventing the casing area, crairpassage, from beingcomplete- 1y closed.. The lposition of the stop pinwill be determinedfrom the pressure volume and horsepowercharacteristics of the particular fans to which the guide vanes areapplied. as describedv above.

It will be seen thatmy novel adjustable guide vanes redirect the airfrom the first stage fan to-t ward any following stage to thereby'effectively multi-stage a plurality oi' fans and provide` a means foreffectively regulating the volume of air multi-stage fan unit withoutoverloading the motor driving the fans, by varying o1' the minimum airvolume I Oad which I vthe magnitude of the rotational component of theair entering a following stage fan.

It will of course, be understood that the fan I2 such as shown .give tothe air tangential component the magnitude of which provided with sureof the air delivered by a simple or single may be omitted to therebyprovide a simple or singleA stage fan having adjustable guide vanes, inFigure '7, arranged adjacent the inlet side thereof. the surfaces ofwhich vanes entering the fan a rotational and may be varied by changingthe position of the guide vanes relative to the fan to thereby provide anovel volume pressure regulating means for a simple or single stage fanwhich will not :overload the motor driving such fan as the volume of airdelivered is decreased.

Referringnow to Figures 5 and 6, I have shown therein, a modication oi'the means for actuating my combined guide vane and pressure volumeregulating means.

In order to rotate the guide vanes 58, about the sockets 68 arranged onthe motor body 62, I provide the radial shafts 84, fastened to the guidevanes, with the pinions 88 which are secured to the shaft ends 88,extending above the casing, through suitable openings NI arrangedthereon.

The pinions rack gear 12, arranged on one face of the sleeve 14, whichis slidably arranged on the casing 18, and which is provided on theopposed face with the ring 18. Fixedly secured to the casing, by therivets 88, I arrange the coupling 82, which is the annular flange 84,having the sleeve ring retaining wall 88 depending therefrom to providean annular channel 88l in which the sleeve ring is slidable.

As the sleeve is rotated on the casing by means of the handle bar 88,extending therefrom, the gear rack and pinions coact to rotate the guidevanes into any desired position, and to thereby regulate the air. volumeand pressure delivered by; the fans in the manner heretofore described.

It will be understood. that a friction drive, belt and-pulley, or anyother suitable arrangement may likewise be used for my novel fan airpressure and volume regulator.

It will be seen that I have provided a novel means for eilectivelymulti-staging propeller fans, and which means are `adapted to providepressure volume air regulation of said fans without overloading themotor driving the fans.

operatively engagethe annular It will be further seen that I have alsoprovided means for regulating the volume and presstage fan, whichregulating neanswill not overload the motor driving the i'an as the airvolume delivered is decreased. f c

While I have shown and described certain speciilc embodiments of myinvention, it will be understood that I donot intend to limit myselfthereto but desire to claim my invention as broadly as may be permittedby the state of the l priorart andthe Scope oi' the I claim:

1. "Ihe combination with a casing of a plurality oi' fans for generatinga stream of air arranged in the casing, means for driving the fans, thesaid stream of air having imparted thereto a generally forwardrotational motion in the nature of a forward moving'spiral by one of thesaid fans, and means intermediate the fansl appended claims.

a multi-stage fan,` 5 'I6 plurality of guide vanes whereby air atcomprising a plurality of blade units,

air stream pressure volume regulatingmeans for said multi-stage fan,said fan driven by said motor and said regulating means comprising aadjustable about an axis disposed angularly to-the fan shaft andarranged intermediate the fan stages, whereby the motor power requiredto drive the fans is directly proportional to the volume of airdelivered.

3. In combination, a motor, a multi-stage fan air stream pressure volumeregulating means for said multistage fan, said blade units rotating inthe same and driven by said direction at constant speed motor, and saidregulating means comprising a plurality of guide vanes adjustable aboutan axis disposed angularly to the fanI shaft and arranged intermediatethe blade units, whereby the power required to drive the motor and fandecreases as the volume of air delivered by the fan is thereby decreasedand means for limiting the adjustment of the said guide vanes.

4. In a device of the character described, a casing, a plurality of fansarranged in the casing, means for driving the fans, air volumeregulating means comprising a plurality ofguide vanes rotatable about anaxis disposed angularly to the fan shafts and secured to the casingintermediate the fans and gear means for rotating the guide vanes intoselected positions whereby air at predetermined volumes corresponding tothe position of the vanes is delivered by the fans.

5. In a multi-stage fan, the combination with a plurality of fans,'ofmeans fordriving the fans, a guide vane rotatable about an axis disposedangularly to the fan shafts and arranged intermediate the fans and meansfor selectively positioning the guide vane relatively to the fanspredetermined volumes correto the position of the guide vane sedeliveredby .the fan and the power of the `fan driving means is an spondinglected is requirements increasing function of the volume of airdelivered `disposed .by the volume by the fans.

6. In a multi-stage fan, the combination with a plurality of fans fordelivering air, one of the said fans imparting to the air delivered byit a rotational forward motion, of means for driving the fans and meansadjustable about an axis angularly td the fan shafts and adjacent saidfan for variably adjusting the rotational component of the imparted airmotion. before the air is delivered to the other fan, whereof airdelivered by the multistagefan may be adjusted, said multi-stage fanhaving a decreasing horsepower characteristic with decreasing volumes ofair delivered by the fan.

'7. In a device of the character described, a easing, a plurality offans arranged in the casing and rotating in the sameI direction, meansfor driving the fans, a plurality of guide vanes operatively arranged inthe casing intermediate the fans and adapted to be selectivelypositioned therein about an axis disposed at an angle to the fan shaftsand to thereby variably restrict the easing area, and means foroperating the vanes, whereby the volume of air delivered may be adjustedselectively and the power requirements of the fan driving means beingthereby of an increasing function of the air delivered by the fans, saidmaximum restriction of the casing area.

8. A device of the character described comprising a casing, a pluralityof fans arranged in the casing, a motor peratively connected to themeans horsepower vanes arranged to limit the l fans and meansforyregulating the volume of air delivered by the fans including guidevanes adjustable about an axis disposed at an angle to the fan shaftsand arranged intermediate the fans and adapted to be positionedrelatively to the fans whereby the motor horsepower required to drivethe fans decreases as the volume of air delivered by the fans is loweredby the selective positioning of the guide vanes.

9. The combination with a casing of a plurality of propeller fans drivenat constant speed arranged in the casing, means operatively connected tothe fans for driving the fans and means for regulating the volume of airdelivered by the fans, said volume regulating means being arrangedintermediate the fans and adapted to be selectively positionedrelatively thereto to thereby selectively regulate the-volume of airdelivered bythe fans whereby the fan driving means horsepower decreasesas the volume of air delivered by the .10. The combination with a casingof a plurality of propeller fans arranged in the casing, meansoperatively connected to the fans for driving the fans, means forregulating within a fans is selectively decreased. Y

selected range the volume of air delivered by A thereby selectivelyregulate the volume of air delivered by the fans is selectivelydecreased.

1l. The combination set forth in claim 10 and including means forlimiting theV position of the volume regulating means.

12.-'I'he combination with a plurality of propeller fans driven atconstant speed of guide vanes adjustably arranged intermediate the fans,said vanes adapted to be selectively positioned relatively to the fans,to thereby provide means for regulating the volume of air delivered bythe fans whereby the motor horsepower required to drive the fansdecreases as the volume of air delivered by the-fans is lowered by theadjustment of the guide vanes, any selected position of the guide vanescorresponding to a predetermined air volume fandelivery.

13. In a device of the character described, a

casinga plurality of fans arranged in the casing, a plurality of guidevanes swingably secured in the' casinglintermediate the fans, a sleeverotatably arranged on the plurality of slots and an arm secured to theguide vanes and engaging the slots, whereby the guide vanes are swung inthe casing upon rotation of the sleeve on the casing.

14. In a device of the character described, a. casing, a plurality offans arranged inthe casing, a plurality of guide vanes the casingintermediate the fans, a sleeve rotatably arranged on the casing, andmeans operatively connecting the sleeve and the guide varies whereby theguide vanes areswung in the casing on rotation of the sleeve on thecasing.

15. In a device of the casing, a plurality of fans arranged in thecasing, a plurality of guide vanes adjustably arranged in the casingintermediate the fans, a sleeve rotatably arranged on the casing and alinkage arrangement connecting the sleeve vanes whereby the guide vanesare adjusted in the casing on rotation of the sleeve on the casing.

16. In combination, a casing, a constant speed propeller fan arranged insaid casing and adapted swingably secured to and the guide v casing andprovided with a character described, a l

volume oi' air forced through the casing.

17. The combination with a casing of a constant speed propeller fanarranged in the casing Vand means for regulating the volume of airdelivered by the fan, said volume regulating means adapted to bepositioned within the casing about an axis perpendicular to the fanshaft relatively tothe fan to impart a rotational motion of selectedmagnitude to the air directed toward the fan and to simultaneouslyincrease resistance of the air ow therepast whereby the power requiredto operate the fan, within defined air delivery limits, decreas'es withthe volume of air delivered by the fan as it is selectively decreased.

18. The combination set forth in claim 17 and including means forlimiting the position ofthe volume regulating means. s Y 19. Incombination, a casing, a constant speed propeller fan arranged in thecasing and adapted to force air therethrough, a plurality of vanesswingably arranged in the casing adjacent the inlet side of the saidpropeller fan, a sleeve ro-l tatablyarranged on the casing and providedwith a plurality of slots and an arm secured to the guide vanes andengaging the slots, whereby the rotating the guide vanes into selectedpositions whereby air at predetermined volumes corresponding to theposition of the vanes is delivered by the fans.

21. A multi-stage ian comprising a casing, a plurality of propeller fansarranged in the casing, a motor operatively connected to the fans andadapted to rotate them in the same direction and means for regulatingthe volume and direction of the air delivered by the fans includingguide vanes adjustably mounted within the casing on the inlet side ofthe following stage fan and adapted to be adjusted to regulate thevolume and direction of the air in the casing whereby tbemotor'horsepower requLed to .drive the fans decreases as the volume ofair delivered by the-fans is decreased bythe selective adjustment of thesaid guide vanes.

22. 'I'he combination set forth in claim 21 and including means mountedon the exterior of the casing and connected with the guide vanes wherebythe position of the said guide vanes may be simultaneously adjusted.

ALFRED E. SEELIG.

